The fiery explosion of a propane tank on a food truck in Philadelphia raises questions about safety regulations for mobile kitchens.

A mother and daughter working onboard the La Parrillada Chapina food truck were critically injured when one of the canteen’s two four-foot propane tanks exploded, engulfing the truck in a flames on Tuesday evening, Philadelphia Police Chief Inspector Scott Small said. Nine other people, including the occupants of two cars driving by at the time of the explosion, were hospitalized.

The fireball engulfed the truck and reached the other side of the street, where it ignited a telephone pole, but it did not reach adjacent homes and businesses. Surveillance cameras from two nearby businesses caught the explosion on video. The Philadelphia fire and police departments, as well as a bomb squad, are investigating whether foul play might have been involved, Chief Inspector Small said.

Food trucks and mobile canteens have been around for decades, but the industry has taken off in recent years as would-be restaurateurs ride a national tide of interest in freshly prepared, specialty foods on wheels – faster and often cheaper than what's available in nearby brick-and-mortar businesses.

Moreover, the advent of iPads and mobile credit-card readers that connect to cellular networks have untethered entrepreneurs from traditional cash registers. Recently, established restaurants, damaged by the competition, have entered the game.

Data from Los Angeles-based industry analyst IBISWorld suggest that the mobile canteen sector has grown an average of 8.4 percent a year over the past five years, the Monitor’s Kendra Nordin reported in August. The small-business research and consulting firm Emergent Research, in Lafayette, Calif., predicts that annual food truck revenue will top $2.7 billion by 2017, Ms. Nordin reported.

Today’s food trucks are a different beast from the refrigerated sandwich trucks that have pulled up next to construction sites and large office buildings for years. This new breed of food trucks doesn’t just serve up soggy sandwiches and reheated meals. Many vendors offer locally produced, gourmet-quality food from lamb barbecue to lobster, some with organic, vegan, and gluten-free options.

While food trucks of yore might have had a microwave or a hot plate to heat food, many of today’s trucks contain full-blown kitchens to satisfy the increasingly sophisticated palate of the American consumer. With kitchens, come fuel, and – as the explosion in Philadelphia illustrated – with fuel come fire hazards.

Municipalities have existing regulations relating to food safety, sanitation, and waste disposal. Many cities have adopted additional rules pertaining to heat and fuel sources, and those regulations vary from city to city. In Boston, for instance, proprietors of “walk-on vehicles” who cook, prepare, and serve food must pass a fire inspection and obtain an open burning/cooking permit.

The city of Chicago requires mobile food vehicles equipped with propane or natural-gas systems or generators to submit to inspection by the Chicago Fire Department. In Philadelphia, where Tuesday night’s explosion took place, an applicant for a mobile vending permit must disclose all equipment to be installed in the truck and provide details for all power sources used to run ovens, fryers, refrigerators, and other appliances.